260 COAL-TAR DYES 



In early days this coal tar was a source of great annoyance 

 to gas companies : they did not know how to get rid of it. 

 We know now, and the enormous quantities we produce are 

 one of our most precious sources of wealth. 



When coal tar is subjected to dry distillation, i.e. put into 

 a closed retort and heated, there issue from it vapours which, 

 on being passed through a spiral pipe and cooled, condense 

 into various kinds of oils. 



The first oils which are condensed are called light oils ; 

 then, as the temperature of the retort is increased, various 

 heavy oils, known as carbolic oils, and creosote oils, and 

 anthracene oils are obtained. 



On further distillation the light oils yield among other 

 products Benzene. 1 It is a clear, colourless liquid, which, 

 when acted upon by nitric acid, produces nitro-benzole, 

 which again when treated with nascent hydrogen produces 

 Aniline, a combination of carbon, hydrogen, and nitrogen. 



Aniline 2 is itself a colourless, oily liquid, but, when acted 

 upon by various other chemicals, it produces many compounds 

 of beautiful colours, known as aniline purple, aniline green, 

 aniline magenta, &c. 



Aniline had been discovered in 1826 as a product of the 

 dry distillation of indigo ; it was called aniline from the 

 Spanish anil, this being the name given by the Spaniards to 

 the indigo plant of the West Indies. 



But though aniline existed it was very rare and costly, 

 and found only in a few scientific laboratories : it was only 

 after Perkin discovered that it could be obtained from coal 

 tar that its use became a commercial possibility, but from 

 1856 onwards its production has constantly increased, and 

 aniline dyes have tended more aAd more to take the place of 

 the older vegetable dyes. 



When the Aniline Mauve was first introduced, the silk dyers 3 



1 Benzine C 6 H C . 2 Aniline C,H 7 N. 



3 Sir Robert Pullar on seeing the first specimen wrote : ' If it is possible 

 to apply that in a practical way it should be a very valuable thing.' 



